A major challenge in the area of plant growth control is to learn how protein assemblies inside the cell influence the mechanical properties and spatial patterns of the cell wall and its growth. Biologist Daniel B. Szymanski and Mechanical Engineer Joseph Turner joined forces to create a realistic computational model that reveals new insights into which cell wall mechanical properties are most important during cell growth. The research, which was recently reported in Nature Plants, also shows how protein assemblies allow these cell wall patterns to be generated and maintained during the growth process. Plants are sessile organisms; however, they grow rapidly over time to establish a body plan that enables efficient conversion of sunlight into biomass. Individual cells are the building blocks of the plant. As they grow, they collectively determine the size and shapes of important organs like leaves, stems, and roots. If researchers are able to discover the key control modules and growth mechanisms of plant cells, it would become possible to use modern genetic technologies to create new types of crop plants with customized architectures and chemical compositions.

In this paper, the team shows that an evolutionarily conserved module of signaling and cytoskeletal proteins generates a meshwork of actin cytoskeleton filaments near the cell apex. This apical actin meshwork organizes actin bundles that act as roadways which span the entire cell. The actin “roadways” transport the raw materials that are needed to support cell growth. Actin is known to influence growth indirectly by modulating the mechanical properties of the cell wall; however, the exact mechanism is unknown. By combining live cell imaging of dozens of cell growth parameters with a computational mechanical model of the cell wall, the team was able to learn how the apical actin patch influences cell wall thickness and mediates the normal shape change process in this cell type. These results not only will have a broad importance for the engineering of cell types like leaf trichomes and cotton fibers, but also provide a framework to understand how the actin and microtubule cytoskeletons cooperate to dictate plant cell growth mechanisms. The computational models created as part of this project will be used as a new type of tool to focus experimental work on biological processes that are important for plant productivity in both natural and agricultural settings.

This research project was conducted by Post-Doctoral Associates Makoto Yanagisawa and Anastasia Desyatova, with the assistance of graduate student Samuel A. Belteton and research technician Eileen L. Mallery. It created educational opportunities in which a diverse team of biologists and engineers at very different levels of experience attacked an important biological problem. This new collaboration accelerated the rate of discovery and provided new insights into plant growth that otherwise would not have been possible. As a result of this project, engineering students have been pulled toward biology, and biologists have a greater interest in using computational tools.